Compositions for the preparation of heat-resistant insulating materials, particularly in the form of independent films



COMPOSITIONS FOR m PREPARATION OF HEAT-RESISTANT INSULATING MATE- BIALS, PARTICULARLY IN FORM OF INDEPENDENT Oscar Kenneth Johannlon. Co

.signor to Corning Glass a corporation of New Yo j No Drawing.

, N. Y., as-

rning Xorks, Corning, N. Y.,

Application Feb"!!! 28, 1945, I Serial No. seam s Claims. (01. zen-1s) This invention relates to compositions of matter for use in the production oi coatings, fllms and plastics which are characterized by their ability to withstand elevated temperatures. 'More particularly, it deals with heat resistant insulating materials and methods of making them.

It is generally recognized that conventional organic films, coatings and plastics are limited in their utility by temperature and that they cannot be used for continuous service at temperatures over about 150 C. This limitation puts a considerable restriction on safe service temperatures of many insulating materials and has particularly put a temperature limit on the design of electrical equipment.

In the construction of electrical apparatus large amounts of electrically insulating material are required. In certain applications, the insulation 2 conventional machinery. A further object isto provide such tapeor sheet'insulation having the property of becoming thermally cementitious,

. structions.

is applied by winding or shaping to some predetermined form in order to accommodate coils or other electrical conductors. In order to avoid the temperature limitations of typical organic insulations such as paper, shellac, and cellulose derivative films, designers have used inorganic spacing materials such as mica sheets, glass fiber cloth and fibrous asbestos.

There has long been a need for a flexible electrical insulating material which can be provided as a continuous sheet or tape, which can be used in thin sections and which will withstand relatively elevated temperatures without substantial deterioration in its insulating characteristics. Mica has been employed widely in thin sheets but requires a high proportion of hand labor in utilizing it either as splittings or in the manufacture of laminated insulating materials. Glass filaments and threads, alone or woven into cloth and tapes, provide insulation which can be handled by winding machinery but loses insulation resistance when wet due to moisture penetration of the interstitial spaces. Fibrous asbestos is sub- 7 ject to similar objections and is further bulky to use. The primary object of this invention is to provide a composition of matter capable of yielding fllms coatings and plastics characterized by their resistance to deterioration at elevated temperatures and by their flexibility and toughness at application temperatures.

It is a particular object of the invention to provide a flexible heat resistant insulating material in the form of a free fllm which can be slit into wrapping tapes and which will have sumciently good mechanical propertia to permit easy winding on coils, bars, and other conductors by thereby permitting the conversion of wrapped insulation to a sealed, unitary covering over the conductor or coil, or providing a laminating film for use in the production of other insulating con- Another object of the invention is to provide a thin flexible insulating material which may be used in condensers, capacitors and the like at elevated temperatures. A further object is to provide a method of insulating conductors with heat resistant continuous insulation.

Other objects include the provision of articles of manufacture useful in the design of electrical equipment to operate at temperatures above those considered safe for conventional organic insulations.

These and other objects not specifically set forth will become apparent in the detailed description and examples of the invention given below.

I have now found that the above mentioned and related objects can be attained to an unexpected degree by employing compositions of matter comprising certain organo-silicon oxide condensation polymers and solvent soluble cellulose ethers.

In carrying out the invention, the organosilicon oxide product is prepared in a stage of condensation at which it is still dispersible in organic solvents. A solution of the said silicone is added to a solution of the cellulose ether in a common solvent to yield a clear compatible fllm forming composition. Coloring matter, pigments,

, fillers or finely divided dielectric solids may be added as the application demands. The composition is then applied to a surface and the solvent removed by evaporation to produce coatings or films. Alternatively, the composition may be freed of solvent in a mixer oi the Banbury type,

lose, butyl cellulose, benzyl cellulose, ethyl benzyl.

cellulose and the like providing that they are freely and completely soluble in aromatic hydrocarbons.

Cellulose ethers alone are limited in their service temperatures by the fact that they become embrittled when heated at temperatures within to C. of their softening point, they tend to carbonize at temperatures above their softening point, and in general. they undergo rapid oxidative degradation at these temperatures. However. compositions comprising the organo-sillcon oxide polymers of the present invention and commercial grades of ethyl cellulose were found to be unexpectedly stable to heat, even when the ethylcellulose constituted a major part of the composition and the film or coating had been subjected to temperatures well above the softening point of the contained ethylcellulose.

When such compositions are heated, they soften and become deformable at temperatures from 100 C. to 200 0., depending upon the resin content and its degree of condensation. Each composition has a temperature threshold above which it softens enough to become heat sealable or fiowable under slight pressure. Further heating above this point generally results in conversion of the composition to an infusible, heat resistant state. It is likely that the stabilization of the ethylcellulose by the organo-silicon oxide polymer is due to the fact that the latter enters into combination with the former through some condensation mechanism not fully understood. In any event, the heated compositions are no longer soluble in the same solvents. Further, they are infusible, or at least much higher in their melting point, and are surprisingly more stable at elevated temperatures than would be expected considering their content of products based upon carbon as the essential structural element.

The organo-silicon oxide polymers for use in the film forming compositions of this invention are those which are derived from compounds of the general formula RSiXz, by hydrolysis. It represents any monovalent hydrocarbon radical attached to silicon through carbon-silicon linkage and X represents .a halogen, alkoxyl, or other hydrolyzable group. The hydrolysis products of these compounds are capable of condensing in three directions as follows:

I II III IV The exact structure of the condensation polymers represented by Formulas III and IV is not known but they are believed to consist of rings built up of groupings. It is also likely the completely hydrolyzed primary product in Formula II rarely exists as such but is converted as fast as formed into polymeric products by elimination of the elements of water between two or more molecules. Between the simple compounds of Formula II and the ultimate condensation polymers of Formula IV, there are formed condensation polymers having an infinite range of molecular sizes and configurations depending upon the conditions of hydrolysis and condensation.

When the hydrolyzable group X is alkoxy, the condensation polymers of this invention include intermediate hydrolysis and condensation products which may still contain appreciable amounts of unhydrolyzed alkoxy'igroups, i. e., up to about one such group per silicon atoms. When the hydrolyzable group x is halogen. it is necessary to remove all halogen completely to avoid development of free acid on heating the film composition and its consequent embrittling eflects on the cellulose ether.

The organo-silicon oxide polymers of this invention may also be derived from mixtures of compounds having the general formula asnx: defined above, that is, two or more compounds of this type wherein the hydrocarbon radicals are different. Hydrolysis of such mixtures and condensation of the hydrolysis products result in copolymeric compositions wherein the unit structure n+0 is linked to different unit structures of the formula as-described by James Franklin Hyde in his copending application, Serial No. 432,528. Such copolymeric compositions may be handled and treated for the purposes of this invention in exactly the same way as the polymeric products described above.

The condensation polymers or copolymers of this invention are limited to those which are still soluble enough in aromatic hydrocarbons to give a gel-free viscous solution. Such polymers, on removal of solvent, are capable of condensing further on baking at elevated temperatures to a substantially insoluble and intusible state. I have discovered that such polymers are compatible with ethylcellulose both in solution and when laid down as a free self-supporting film. The films so obtained are coherent, flexible and water-impervious and possess desirable electrical properties as well. In general, I prefer to limit the amount of ethyl cellulose employed to about 60% and to use at least about 15%. The resulting films are not only flexible but also have a relatively high thermal stability.

Examples of the monovalent hydrocarbon radicals which are represented by the symbol R in the general formula RSiXa, given above, are as follows: methyl, ethyl, propyl, isopropyl, butyl, isobutyl, amyl, hexyl, heptyl to octadecyl and higher; alicyclic radicals such as cyclopentyl, cyclohexyl, etc., aryl and alkaryl radicals such as phenyl, monoand poly-alkyl phenyls such as tolyl, xylyi, mesityl, mono-, di-, and tri-ethyl phenyls, mono-,. di-, and tri-propyl phenyls, etc., naphthyls, monoand poly-alkyl naphthyls, as methyl naphthyl, diethyl naphthyl, tripropyl naphthyl, etc.; tetra-hydro-naphthyl, anthracyl, etc.; aralkyl such as benzyl, phenylethyl, etc.; alkenyl such as methallyl, allyl, etc. The above radicals may contain inorganic substituents such as halogens, etc.

For a better understanding of my invention, reference should be had to the following ex amples:

Example 1 A sample of methyltriethoxysilane was hydro lyzed by adding twice the theoretical amount of water (3 moles per mole MeSi(OEt) a) to the ester, at room temperature, using a trace of HCl as catalyst. The product dried to a tack-free state at room temperature. Films, on copper, were brittle and cracked on slight flexing. After as much as a week of air-drying on copper the films would gather and become chalky, when placed in hot water. Baking improved their resistance to.

hot water but made them more brittle, Grazin sometimes occurred during the baking; for instance, crazing occurred in two to six hours at 180 C. with films on glass plates.

on mixing the above resin with one-third of its weight of ethyl cellulose B, medium viscosity, a. product was obtained which was homogeneous and yielded clear films. On airdrying on a copper base the films would withstand repeated flexure, even when bent back upon themselves. Films on glass were heated twelve hours at 180 C. without crazing. Films on this glass, baked three hours at 180 (2., did not whiten during a'twenty hour immersion in hot water. Mixtures containing 10, 50, 75 and 90 per cent by weight of ethyl cellulose, were also examined at this time. The organo-silicon oxide resin and ethyl cellulose were compatible in all cases. As the ethyl cellulose content of a mixture was increased; the following effects were noted: the flexibility of films, which had been heated one hour at 180 C. was greater; however, color after heating was more marked; whitening and loss of adhesion to glass, on immersion in water, became greater.

It was also noted that solutions of the organosilicon oxide resin, which contained ethyl cellulose, could be stored for longer periods of time without gelling, than could solutions which did not contain ethyl cellulose. The mixture containing 25 per cent by weight of ethyl cellulose, was still fluid after six months storage.

Example 2 To 200 g. of methyltriethoxysilane, 60.6 g. of water was added, using a trace of HCl to catalyze the hydrolysis. A part of this was mixed with high viscosity ethyl cellulose, to give a mixture containing per cent by weight of the latter. Aluminum powder was added to give a pigmentvehicle ratio of 1/2 on a weight basis. After thinning with dioxane, the paint was brushed onto iron panels. Films of this paint were intact after 1 /2 hours at 250 C. and protected the metal well. Air-dried films on iron were good after eight months exposure to the weather. With the same pigment-vehicle ratio, but with no ethyl cellulose present, a paint film was soft and had collected a considerable amount of dirt, after five months exposure to the weather.

Example 3 Methylsilicic acid resin, prepared as given under Example 2, was mixed with high viscosity ethyl cellulose B, to give a mixture containing 25% by weight of the latter. This was mixed with ochre, to give a pigment-vehicle ratio of 1/2. Applied as a paint to iron, it was in good condition after fourteen days exposure to a Hanovia sunlamp. Without the ethyl cellulose, the body of the paint, even at high concentrations of the organo-silicon oxide resin, was too thin to be brushed on satisfactorily. The ethyl cellulose gave an improved body, i'a-ster drying, and better gloss.

Paints from the methylsiliclc acid resin and ethyl cellulose were also prepared using red lead and ultramarine as pigments.

Example 4 A solution of 163.5 g. of C2H5SiCl3, in 200 ml. of ether, was added to 618 g. of an ice-water mixture. The solution was washed to neutrality and ether was removed under reduced pressure. The resin obtained had a hydroxyl content of 10.2%.

A 25% solution of the resin at 70:30 tolueneisopropanolwas prepared. Portions of this solu- Medium-ethoxy Ethocel, viscosity 20 Standard-ethoxy Ethocel, viscosity 20 High-ethoxy Ethocel, viscosity 300 Low viscosity-ethyl cellulose B Medium viscosity ethyl cellulose B High viscosity ethyl cellulose B From the solutions or the mixtures, films were cast on microscope slides; these air-dried to thicknesses ranging from 1 to 2 mils. All mixtures air-dried tack-free, to give clear colorless I films, which were suflitiently flexible to be bent over a 2 mm. mandrel. The air-dried films were soluble in toluene. The rates of solution and the extent to which solution occurred was markedly decreased by a ninety minute bake at 150 C.

Example 5 To 0.83 g. of a 10% solution of medium-ethoxy Ethocel in 70:30 toluene-isopropanol, 1 gram of a solution of the resin of Example 4 was added. This gave a mixture 25% in Ethocel. After thorough mixing, films were cast on glass. The films were tack-free after a 15 minute airdry. By immersing coated glass plates in water for one hour, the films could be separated from the glass base. Films, on glass, heated 90 minutes at 150 C., were strongly adherent and were not removed by a ninety minute immersion in water.

Example 6 A mixture of the resin of Example 4 and medium viscosity ethyl cellulose B, 75% in the latter, was prepared. The film obtained on air-drying,

could be bent over a 2 mm. mandrel without breaking. After such drying, the material was entirely soluble in toluene, dissolving within five minutes. Films of the material baked for minutes at (2., swelled in toluene, within 15 minutes, but were largely undissolved after 17 hours in the solvent.

Example 7 A sample of the resin of Example 4 was partially dehydrated by heating a xylene solution to reflux for two days. The solvent-free product contained 2.1% OK. It was compatible with all six types of ethyl cellulose, listed in Example 4, in mixtures 25, 50, and 75 per cent in ethyl cellulose. The following are illustrative of the compositions obtained:

- To 0.83 g. of a solution of high viscosity ethyl cellulose 13, in 70:30 toluene-isopropanol, 1 gram of a solution of the'above partially dehydrated product in the same solvents, was added. The mixture containing 25% by weight of ethyl cellulose, was homogeneous and gave homogeneous films when cast and air-dried on micoscope slides.

Fflms, after baking for one hour at C., were removed from the glass and were found to be sufliciently flexible to be bent over a 2 mm. mandrel, without breaking. A fllm, after such a bake, was intact though swollen, after 48 hours in toluene.

Mixtures containing 50 per cent by weight of standard-ethoxy Ethocel and 50 per cent of the above resin were prepared by mixing appropriate amounts of solutions of the two materials, then casting, and allowing the solvents to evaporate. Films were clear and colorless. They could be bent over a 2 mm. mandrel, without breaking,

ether, was shaken with concentrated HCI.

7 after a one hour bake at 170 C. After such a bake. the aims swelled in toluene, but did not dissolve.

of the resin without ethyl cellulose were so b tie, after heating one hour at170 C., that they could not be removed from the glass base on which they were cast, without flaking.

Example 8 Example 9 A 50% solution of the resin of Example 8 in The ether solution was washed to neutrality. This treatment reduced the hydroxyl content of the solvent-free resin from 4.9% to 4.3%. The resin was compatible with high-ethoxy Ethocel and high viscosity ethyl cellulose B, in mixtures containing 50 and 90 per cent by weight of ethyl cellulose. The mixtures dried tack-free. They retained their shape, when heated as free films, at 160 C. After four hours at this temperature, the films (1-2 mils thick) could be creased without breaking.

I claim:

1. A composition of matter which comprises 40 to 85 per cent by weight of a resinous polymeric organo-silicon oxide condensation product consisting of structural units which correspond substantially to the general formula RsiOa a where R. is a lower alkyl radical and 15 to 80 per cent by weight of ethyl cellulose having from 2.25 to 2.75 ethyl groups per anhydro-glucose unit, said ethyl cellulose being completely soluble in an arcmatic hydrocarbon and said condensation product being sufllciently soluble in an aromatic hydrocarbon to give a gel-free viscous solution.

2. A composition of matter which comprises 40 to 85 percent by weight of a resinous polymeric organo silicon oxide condensation product consisting of structural units which correspond substantially to the general formula CHaSiOa a and.

15 to 60 percent by weight of ethyl cellulose having from 2.25 to 2.75 ethyl groups per anhydroglucose unit, said ethyl cellulose being completely soluble-in an aromatic hydrocarbon and said condensation product being sufllciently soluble in an aromatic hydrocarbon to give a gel-free, viscous solution.

8. A composition of matter which comprises 40 to 85 percent by weight of a resinous polymeric organo silicon oxide condensation product consisting of structural units which correspond substantially to the general formula CzHeSIOan and 15 to 60 percent by weight of ethyl cellulose having from 2.25 to 2.75 ethyl groups per anhydroglucose unit, said ethyl cellulose being completely soluble in an aromatic hydrocarbon and said condensation product being sufllciently soluble in an aromatic hydrocarbon to give a gel-free viscous solution.

OSCAR KENNETH JOHANNSON.

naranancas crran The following references are of record in the file of this patent:

UNITED s'ra'rns Perms 

